층 = tier, layer
For buildings, 층 can mean
floor (as number of floors/storeys), should be used with korean numbers but the rule is not followed rigidly.
counter for floor-level (floor number, ~th floor), used with sino-korean numbers
The use of numbers associated with 4 s.a. 14, 24, 49 etc. is discouraged in some buildings because of old superstition.